Realization of a 7-way FM dual frequency change

 

The receiver remains a rather expensive (especially when you are a student), yet it is useful to have more as soon as we have different models. So I decided to make my receivers to equip different gliders, to have them ready to fly, and avoid the many manipulations often fatal to the connectors, and antenna. But my motivation comes mostly from my passion for electronics.

Specifications:

The receiver will have seven lanes on FM. It will double the frequency change to fully reject the image frequency components used to make a modern double change with only a few additional components to a simple change.

Wanting a reliable, simple to perform and economical, I can not remember a version with integrated microcontroller for PCM encoding or frequency synthesis.

Technology choices:

The work is fairly simple, in fact there is now integrated circuit incorporating the most powerful features in one box. Based on article by Serge LAFOREST I opted for the Motorola 3335. The manufacturer offers a number of circuits dedicated to FM receivers. The 3335 is a component in "late career", but its price is attractive (below 30F), and its performance is still valid. There are no unnecessary features to our application, in short it has less leg than the other. Decoding is given to a classic 4017. I took little difference in the pattern of Serge (Serge Thank you for your article).

The receiver is realized with conventional components (through-) except for 4017 which is in CMS. This gives a realization in everyone, and the circuit is small.

Compared to the model Serge I made some changes (I do not have priority weight):

• The input filter consists of two pots 2K159 to obtain better filtering in the receiver input.
• The circuit can include a choice of a pre-amp HF between the two pots (BF200 transistor) to obtain a better range. I realized the two versions (with and without preamp) without finding significant differences. The sensitivity is slightly better with the preamp. With the unfiltered version, I've never had a top radio, and the scope seems to be largely sufficient. Unlike many ideas, have a receiver may be too sensitive an issue for the model, since the receiver becomes more sensitive to other issuers? In addition, the transistor "charge" the pot input and therefore decreases the effectiveness of the filter (it is less selective). In conclusion, the preamp provides a gain of stew, but increases the risk of saturation of the receiver by a nearby transmitter.
• The filter 455 is an IT (m 2 KHz-6dB) compared to that used by D Serge, gives me a very good selectivity, and reach much higher (better signal to noise?). I think the D (bandwidth greater than 10KHz) seems useless, especially if you fly to several in the same band. A HT will also be the case (m 3 KHz-6dB).
• The receiver power is filtered through a large capacity and is a transistor that provides as a protection circuit in case of polarity reversal of power.
• Finally, the circuit includes seven connectors (pin Graupner, Hitec) performed with the support of circuit wrapper.

Manufacturing:

It is open to all (well, those who have touched a soldering iron!). It will take care of the seams and starting with the 4017 CMS. 3335 and then solder the other components. Do not forget the filter via nearly 455. Note that you can use a filter or CFW455 CFU455 (pellets were added to allow the use of these two models). For the filter 10.7MHz, leg 1 (landmark on the filter) must be connected to the leg 16 of the MC 3335. The metal boxes and pots HF quartz can be welded to the ground plane to reduce the parasitic capacitances.

The antenna is soldered on the circuit directly on the pot 2K159 (see wiring diagram). It will have a length of about 1m.

For the realization of the connectors, I use the "bikes" to the circuit support wrapper that I cut by three. Drill the holes for these connectors with a diameter slightly less than for the "bikes" come into force. Once taken welded flow of Araldite side seams to guarantee a better mechanical maintains. It is economical and reliable.

Implementation plan components:
Preamp:
Wiring diagram:

 

The preamp is made from a transistor BF200 BF 180 or mounted in common base. The transistor is mounted between the two pots HF.

Board layout:

Without preamp:
wiring diagram:

Both pots are coupled HF through the ability to 1.5pF. This filter is used in many receivers and provides a good selectivity. This selectivity guarantee a "rejection" of the image frequency which is more than 20MHz over the reception frequency on which the filter is given.

Board layout:

It is not welding the components needed to run the preamp (components with a cross). We must add the cons by 1.5pF capacitor. It will be welded in place of the BF200 transistor according to the drawing above (the wiring diagram help when in doubt). 470 W resistance will be replaced by a strap.

Settings:

They are easy to achieve if one has a scope and takes place in two stages:

1. Approaching the transmitter and receiver to a probe at the lug 12 of 3335, (exit demodulation). Turn the ring until the demodulated signal (sequence of about 25ms with the pulses of all channels).
1. Show the signal of the leg 16 of the MC 3335: the first intermediate frequency to 10.7MHz. Adjust the nuclei of two pots of entry to obtain a maximum amplitude of the signal.

Then make tests of reach. Antenna back, we must obtain more than 50m of worn asphalt.

Artwork:

Component side

Solder side

Here are the artwork, I do not know if they are usable from the images above, but if you want to make this receiver, I can provide the printed circuit board (double sided) at a price of 10F + stamped envelope, then n ' Do not hesitate! Supply:

For the purchase of components, here are some addresses:

MC3335P: It is available from Newark which is distributed by Farnell (04 74 68 99 99), also available (a bit more expensive) in Lextronic (01 45 76 83 88 ext 524)

Quartz: This is to tailor. I do realize in Electronics Distribution (03 20 70 23 42). Quartz frequency = frequency of your radio-10.7MHz. This is quartz series resonance of the third harmonic (overtone 3), HC 25 box / U. Of the five controlled quartz I had no problem setting or malfunction.

10,245 Quartz, filters CFW455IT, SFE10.7MS3 pot 2K159, 4017 and all other components are available from Eurocomposant (03 24 27 93 42).

I am at your disposal for any further information: information about some components, with the construction, setting ...

Conclusion:

I fly with this receiver for over a year and never had any problems (Five Models). Yet sometimes we were more than ten to fly with frequencies close to mine, show good selectivity. I think making a receiver is a good experience. If your primary motivation is to save money, we must produce more to amortize the shipping cost and get the lowest price. For the five models currently built the cost is less than 250F per receiver, quartz included!

Happy flying to all and do not hesitate to take the plunge, make your receivers!

Nomenclature

Designation	Order Ref	Price	No.	Supplier
Component "specific"
CFW Filter IT 455	15315	36F	1	Eurocomposants
Filter SFE 10.7 MS3A	05213	5F	1	Eurocomposants
Pot HF 113CN 2K159	05181	12F	2	Eurocomposants
455K Pot demodulation LMCS 4102A Black	05177	12F	1	Eurocomposants
Quartz 10,245 Mhz	05286	10F	1	Eurocomposants
CI CMS 4017BT	16509	5F	1	Eurocomposants
MC 3335 P		30-40F	1	Farnell or Lextronic
Quartz resonant series of 3 rd harmonic Frequency = Fémission-10.7Mhz, case HC18		130F	1	Electronics Distribution
Capacity
1.5pF			1
18-22pF			2
47pF			1
120pF			1
4.7nF			1
47nF			1
100nF			4
4.7μF			1
Resistors
330 Ohms			1
1K			1
1.5K			1
10K			1
22K			1
75K			1
Diodes
1N4148			1
1N4001			1
Transistor
BC 547 or equivalent (NPN)			1
Self
1.5μH			1
Various
Support wrapper> 22 feet for records
1m stranded flexible wire antenna
Option preamp
Transistor BF 200 or 180			1
Capacity 100nF			2
470 Ohm resistor			1
27K			1
8.2K			1